Reconfigurable intelligent surface (RIS)-assisted wireless communication has been proposed as a potential solution for enhancing the energy efficiency of wireless networks [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}. An RIS is a meta-surface equipped with low-cost and passive elements that can be programmed to turn the wireless channel into a partially deterministic space.
In RIS-assisted wireless communication networks, a BS sends control signals to an RIS controller so as to optimize the properties of incident waves and improve the communication quality of users.
The RIS acts as a reflector and does not perform any digitalization operation.
Hence, if properly deployed, an RIS promises much lower energy consumption than traditional amplify-and-forward (AF) relays [13]}, [14]}, [15]}.
However,
the constraint on the diagonal phase shift matrix and unit modulus of the reflecting RIS makes the
joint design of transmit beamforming and phase shifts extremely challenging.
To address high-dimension, complex EM environment, and mathematically intractable nonlinear
issues of communication systems, the model-free FL method as an extraordinarily
remarkable technology can be used.
